var Excel = require('exceljs');
var workbook = new Excel.Workbook();

workbook.xlsx.readFile('Book.xlsm')
.then(function () {
var worksheet = workbook.getWorksheet(1);
var row = worksheet.getRow(1);
console.log(row.getCell(1).value + " - First value"); // Get A1 value
row.getCell(3).value = "c"; //Set value to A3
row.commit();
return workbook.xlsx.writeFile('new.xlsm');
})